Various kinds of impurities including organic substances adhere to a target surface of a target object, e.g., a surface to be processed of a silicon wafer. Such impurities adhering to the target surface contribute to hinder a silicon raw material from adsorbing to the target surface. This degrades a nuclear generation density so that a silicon film having a random rough surface is formed on the surface of the target surface.
To address this, the impurities adhering to the target surface are removed before forming the silicon film. For example, there are known a process method which includes loading a target object into a reaction room (processing chamber), heating the interior of the reaction room at a temperature ranging from 350 to 400 degrees C., and removing impurities adhering to the target object with an oxidizing gas (oxygen gas) and a reducing gas (hydrogen gas), and an apparatus therefor.
In addition, there is known a method of forming a polycrystalline silicon film, which includes exposing a surface of a target object to an ozone atmosphere in a reaction tube, removing molecules adsorbed on the surface of the target object, and forming the polycrystalline silicon film within the reaction tube (processing chamber).
There is a desire to make a silicon film thinner in manufacturing electronic products such as semiconductor integrated circuit devices. However, the existing process performed before forming the silicon film, e.g., a cleaning process or an impurity removal process, contributes to achieve a good surface roughness for a thick silicon film, but causes a deteriorated surface roughness for a thin silicon film. Thus, it is hard to obtain a wanted high precision surface roughness.